The present invention relates semiconductor devices, and more particularly to a guard ring structure providing added protection against diffused ions and noises.
A guard ring is a protective structure encircling part of or an entire active region of a semiconductor device. By biasing the guard rings to a high or a low potential, guard rings provide a barrier to ionic contamination or noise that can penetrate the exposed edges of diced chip during manufacture. Additionally, a guard ring can act as a physical wall to provide mechanical stability to a semiconductor device.
Traditional integrated circuits (ICs) contain multiple circuit sections, each section with different characteristics and functional tasks. Certain sections must be isolated from other sections. Historically, a single chip device contains a single guard ring protecting all active circuit sections regardless of their differing characteristics. Newer techniques use multiple guard rings, especially when the IC contains a mix of digital and analog circuits.
As an example, isolation of these sections is required to reduce noise propagation. In larger ICs, noise travels easily and causes many unwanted and unmanageable noise coupling situations. As another example, a guard ring is used to isolate circuits with different voltage domains. The different voltage domains required by today's high-power transistors with low-voltage control is a cause for voltage-related latch-ups. A latch-up is a condition in which a circuit draws uncontrolled amounts of current, thereby forcing voltages to “latch-up” to an undesirable, uncontrollable level that violates the operating conditions of the circuit.
During the operation of an active device, a flow of electrons and holes is induced by the changes in potential in the components inside the active device. Some electrons and holes stray from the current path and propagate to adjacent active devices, causing faulty activation, performance degradation, or a latch-up of those devices. In order to prevent electrons and holes from propagating to other devices guard rings are used. Guard rings act as well and substrate contact and are biased to collect lose electrons and holes. To reduce the movement of minority carriers, guard rings are further biased for improved performance.
Traditional methods of wiring a guard ring includes connecting a high potential (Vdd) to the N+ doped region within the N well, and a ground potential (Vss) to the P+ doped region within the P substrate. However, such methods are insufficient to deal with the high local dynamic current of the active devices which induces a net voltage drop in the device. Net voltage drop not only results in degraded circuit performance, but also induce circuit failure and/or timing mismatch. As devices become smaller and require less power, this problem worsens. At worst, a net voltage drop may be large enough to render a device inoperable.
Desirable in the art of guard ring designs are additional designs that provide added protection against diffused ions and noise that typically causes latch-up.